Peat filtration of water is known to provide a high level of waste water treatment through physical, chemical and biological processes. Significant reductions in organic carbon, nitrogen, phosphorous, suspended solids, trace metals, and microorganisms can be achieved using peat as a filter. The filter also tends to reduce the pH and increase the dissolved oxygen content of water passing through it. Peat filters for waste water treatment have been in use since the late 1970's.
Presently, when peat is used as component of a treatment system it requires considerable labor and material handling, as well as careful material selection, to construct the peat bed. Peat is obtained at source and is transported either in bulk or in bags to the filtration site. When peat is packed in bags, that are packed to a specific volume (i.e. bag volume), the density of the peat in the bag is variable depending upon the moisture content at the time of packing.
Once at the site, the peat is initially stockpiled until the peat bed of the filtration site is ready to be filled. Loose peat is considerably voluminous and is therefore costly to transport, whereas peat that is bagged involves a considerable amount of labor and cost in handling the bags, namely all of the steps of packing, moving and unpacking.
When a peat filtration site is ready, the peat is added to form a bed in a series of layers. Each of the layers must be raked level to a consistent grade and then compacted to a specific density. One method of compaction is to use people wearing snowshoes to walk over the layers of the peat for long periods of time.
The density is measured by an experienced person who walks over the peat and then measures the depth of penetration of the foot print correlated with mechanically drawn cores of known volume weighed and dried to enable calculation of density. This is a time consuming process and often results are not obtained in a timely fashion to permit rapid installation of successive peat layers. Additionally, meaning the depth of penetration of a foot print is a far from accurate measure. Mechanical coring of the peat is also not entirely accurate due to the properties of the peat. Technicians applying different pressures or handling the equipment differently would have different amounts of peat in the core (i.e. applying different pressures on the sampler will cause the peat to be compressed). The peat bale of the present invention utilizes a known weight of peat packaged to a known volume, thus providing a very accurate density.
Peat is a natural active biological medium and this activity is very important to its suitability as a filter medium. Each successive stage of handling can effect the biological activity and the moisture content and thus variables of installation change on a continuous basis. The monitoring of conditions such as age, moisture content and level of compaction in the peat bed requires highly trained and experienced personnel to closely observe the filling. Even so, the variability of conditions related to handling, installation and peat quality result in difficulty in obtaining optimum performance even with highly trained supervision.
The disadvantages of peat handling and the associated filling of peat filtration beds can be overcome by packing the peat to a predetermined density in a water permeable wrapping such that the bales can be directly used to construct the peat bed. This provides several distinct advantages over present installation method since: 1) the moisture content of peat will be easier to monitor and control; 2) the peat is already compressed in a controlled and reliable manner; 3) there is reduced potential for loss of biological activity during the handling and storage stages; 4) there is reduced potential for contamination of the peat during handling and storage; 5) wastage of peat during handling is eliminated; 6) simplicity of installation is greatly enhanced; and 7) a more uniform level of treatment performance can be achieved.
Prior to the present invention the packaging of peat for use in a waste water treatment system would not have been expected to work. One would have expected, due to the air pockets between the packaged bales, that the water would flow through the cracks between the packaged peat and thus by-pass the treatment media.
U.S. Pat. No. 5,049,265 (Boyd et al.) describes an effluent treatment system that comprises a mixture of young Sphagnum peat and an organic peat fibre in the system. In this system they have included a fibrous material having a relative low absorptive capacity, which reduces ponding or clogging of their system. Thus, according to the teaching of this prior art, effluent treatment system with a high absorptive capacity would not be expected to work, which teaches away from the present treatment system. Also within the Boyd et al. system is an air permeable lid which carries a layer of peat material, which functions to control odor from the system.
The peat bale of the present invention is distinct from and overcomes several disadvantages of the prior art systems, including Boyd et al., as will be discussed in detail below.